Field emission device and field emission display using the same

ABSTRACT

A field emission device and a field emission display (FED) using the same and a method of making the field emission device. The FED includes a glass substrate, a layer of a material formed on the glass substrate and having a concave portion, a cathode electrode formed on the material layer and also having a concave portion, electron emitters formed on the concave portion of the cathode electrode, a gate insulating layer formed on the cathode electrode and having a cavity communicating with the concave portion, and a gate electrode formed on the gate insulating layer and having a gate aperture aligned with the cavity.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationfor FIELD EMISSION DEVICE AND FIELD EMISSION DISPLAY USING THE SAMEearlier filed in the Korean Intellectual Property Office on May 22, 2004and there duly assigned Ser. No. 10-2004-0036669.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel design for a field emissiondevice and a field emission display (FED) using the novel field emissiondevice and a method of making the novel field emission device, the novelfield emission device having improved focusing properties of an electronbeam.

2. Description of the Related Art

Displays play an important role in information and media delivery andare widely used in personal computer monitors and television sets.Displays are usually either cathode ray tubes (CRTs), which use highspeed thermal electron emission, and flat panel displays, which arerapidly developing. Types of flat panel displays include plasma displaypanels (PDPs), field emission displays (FEDs), liquid crystal displays(LCD) and others.

In FEDs, when a strong electric field is applied between a gateelectrode and field emitters arranged at a predetermined distance on acathode electrode, electrons are emitted from the field emitters andcollide with fluorescent materials on the anode electrode, thus emittingvisible light. FEDs are thin displays, at most several centimetersthick, having a wide viewing angle, low power consumption, and lowproduction cost. Thus, FEDs together with PDPs attract attention as thenext generation of displays.

FEDs have a similar physical operation principle to CRTs. That is,electrons are emitted from a cathode electrode and are acceleratedtoward and collide with an anode electrode. At the anode electrode, theelectrons excite fluorescent material coated on the anode electrode toemit visible light. FEDs are different from CRTs in that the electronemitters are formed of cold cathode material. However, a problem withFEDs is limitations in the ability to focus the electron beam so thatthe each electron beam lands at a desired location on the fluorescentmaterial to achieve good image quality.

To overcome this problem, U.S. Pat. No. 5,920,151 to Barton et aldiscloses a FED having an imbedded focusing structure. However, thefocusing gate electrode in Barton '151 is formed on an organic materialcalled polyimide, which requires an outgassing process for dischargingvolatilized gas. Thus, such a FED cannot be applied to large displays.Therefore, what is needed is a design for an FED that provides improvedelectron focus and that can be applied to make large displays.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a designfor a field emission device and an FED using the novel field emissiondevice that results in a tightly focused electron beam.

It is also an object to provide a design for a field emission device andan FED using the field emission device that can be applied to largedisplays.

It is further an object of the present invention to provide a method formaking the novel field emission device and a novel method of making theFED using the novel field emission device that is simple to manufacture.

These and other objects can be achieved by a field emission device thatincludes a glass substrate, a material layer formed on the glasssubstrate and having a concave portion, a cathode electrode formed onthe material layer resulting in a cathode electrode having a concaveshape, electron emitters formed on the concave portion of the cathodeelectrode, a gate insulating layer formed on the cathode electrode andhaving a cavity communicating with the concave portion of the cathodeelectrode, and a gate electrode formed on the gate insulating layer andhaving a gate aperture aligned with the cavity.

The cavity can have a shape of a semicircle or a hemisphere. Thematerial layer can be made of electrically insulating material or madeof a metal, such as the material used to make the cathode electrode. Anamorphous silicon layer having a aperture corresponding to the concaveportion of the cathode electrode can be sandwiched in between thecathode electrode and the gate insulating layer. Being transparent tovisible light but opaque to ultraviolet light, the amorphous siliconlayer can also serve as a photolighographic mask when UV sensitivematerial is to be patterned. The electron emitters can be carbonnanotube (CNT) emitters.

According to another embodiment of the present invention, there isprovided a field emission device that includes a glass substrate, amaterial layer formed on the glass substrate and having a concaveportion, a cathode electrode formed on the material layer, the cathodeelectrode also having a concave portion, electron emitters formed on theconcave portion of the cathode electrode, a lower gate insulating layerformed on the cathode electrode and having a cavity communicating withthe concave portion of the cathode electrode, a lower gate electrodeformed on the lower gate insulating layer and having a lower gateaperture aligned with the cavity, a focusing gate insulating layerformed on the lower gate electrode and having a aperture communicatingwith the cavity, and a focusing gate electrode formed on the focusinggate insulating layer and having a focusing gate aperture aligned withthe cavity.

According to still another embodiment of the present invention, there isprovided a field emission display (FED) that includes a rear substrate,a material layer formed on the rear substrate and having a concaveportion, a cathode electrode formed on the material layer, the cathodeelectrode having a concave portion, electron emitters formed on theconcave portion of the cathode electrode, a gate insulating layer formedon the cathode electrode and having a cavity communicating with theconcave portion of the cathode electrode, a gate electrode formed on thegate insulating layer and having a gate aperture aligned with thecavity, a front substrate spaced apart from the rear substrate by apredetermined distance, an anode electrode formed on a side of the frontsubstrate facing the electron emitters, and a fluorescent layer coatedon the anode electrode.

According to yet another embodiment of the present invention, there isprovided a field emission display that includes a rear substrate, amaterial layer formed on the rear substrate and having a concaveportion, a cathode electrode formed on the material layer, the cathodeelectrode having a concave portion, electron emitters formed on theconcave portion of the cathode electrode, a lower gate insulating layerformed on the cathode electrode and having a cavity communicating withthe concave portion of the cathode electrode, a lower gate electrodeformed on the lower gate insulating layer and having a lower gateaperture aligned with the cavity, a focusing gate insulating layerformed on the lower gate electrode and having a aperture communicatingwith the cavity, a focusing gate electrode formed on the focusing gateinsulating layer and having a focusing gate aperture aligned with thecavity, a front substrate spaced apart from the rear substrate by apredetermined distance, an anode electrode formed on a side of the frontsubstrate facing the electron emitters, and a fluorescent layer coatedon the anode electrode facing the electron emitters.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in a which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a schematic cross-sectional view illustrating the structure ofa field emission device;

FIG. 2 is a schematic cross-sectional view illustrating the structure ofanother field emission device that has a focusing gate electrode;

FIG. 3 is a simulation of the trajectories of electron beams emittedfrom electron emitters of the field emission device of FIG. 2;

FIG. 4 is a schematic cross-sectional view illustrating a field emissiondevice according to a first embodiment of the present invention;

FIG. 5 is a simulation of the trajectories of electron beams emittedfrom electron emitters in the field emission device of FIG. 4;

FIG. 6 is a schematic cross-sectional view illustrating a field emissiondevice according to second embodiment of the present invention;

FIG. 7 is a simulation of the trajectories of electron beams emittedfrom electron emitters in the field emission device of FIG. 6;

FIG. 8 is a schematic cross-sectional view illustrating the structure ofa field emission display employing a novel field emission deviceaccording to the present invention;

FIG. 9 is a simulation of the trajectories of electron beams emittedfrom electron emitters in the field emission display of FIG. 8; and

FIGS. 10 through 22 are cross-sectional views illustrating a process ofproducing the novel field emission device illustrated in FIG. 6according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures, FIGS. 1 and 2 illustrate the structures offield emission devices 11 and 21 respectively. Referring to FIG. 1, thefield emission device 11 has a structure in which a cathode electrode 12is formed on a bottom substrate 10, and a gate electrode 16 forextracting electrons is formed on an insulating layer 14 above thecathode electrode 12. Electron emitters 19 are placed within a hole (oraperture) through which a portion of the cathode electrode 12 isexposed. Opposite the bottom substrate 10 is an anode with fluorescentmaterial on it. Electrons emanating from the electron emitter 19 arriveon the anode to excite the fluorescent layer to thus form visible imagesfor display.

In the field emission device 11 of FIG. 1, if the trajectories ofelectron beams are not controlled, the desired portion of thefluorescent layer cannot be excited, and thus the desired colors cannotbe displayed. Therefore, there is a need for a technique to control thetrajectories of the electron beams, to allow the electrons emitted fromthe electron emitters 19 to be correctly transferred to the desiredportion of the fluorescent material coated on the anode electrode.

Turning now to FIG. 2, FIG. 2 is a view illustrating an field emissiondevice 21 having a focusing gate electrode 28 that controls thetrajectories of electron beams. Referring to FIG. 2, a second insulatinglayer 27 is deposited on a lower gate electrode 26, and a focusing gateelectrode 28 for controlling the trajectories of electron beams isformed on the second insulating layer 27. Reference numerals 20, 22, 24,and 29 represent a substrate, a cathode electrode, a first insulatinglayer, and electron emitters, respectively.

Turning now to FIG. 3, FIG. 3 is a simulation of the trajectories of theelectron beams emitted from the electron emitters of the field emissiondevice 21 having the focusing gate electrode 28 as illustrated in FIG.2. Referring to FIG. 3, overfocused electrons deviate from the intendedregion of the fluorescent layer and excite other regions of thefluorescent layer, reducing color purity.

Turning now to FIG. 4, FIG. 4 is a schematic cross-sectional viewillustrating a field emission device 100 according to a first embodimentof the present invention. Referring to FIG. 4, an insulating layer 112having a concave portion W and a cathode electrode 120 are sequentiallyformed on a glass substrate 110. In FIG. 4, the concave portion W isillustrated as being hemispherical but the present invention is in noway limited to this.

The insulating layer 112, such as a silicon oxide layer, is formed togenerate the concave portion W for the cathode electrode 120.Alternatively, the cathode electrode 120 having a concave portion can bedirectly formed on the glass substrate 110, without using the insulatinglayer 112. The insulating layer 112 can have a thickness of 2 to 10 μm.

The cathode electrode 120 can be an ITO (indium tin oxide) transparentelectrode. An amorphous silicon layer 122 is formed on the cathodeelectrode 120 on portions of the cathode electrode 120 not includingconcave portion of the cathode electrode. The amorphous silicon layer122 ensures a uniform current flow through the cathode electrode 120. Inaddition, the amorphous silicon layer 122 has specific opticalproperties that allow visible light to pass but blocks UV light. Theamorphous silicon layer 122 functions as a mask for a back exposure toUV light, as described below. CNT (carbon nano tube) emitters 150 aselectron emitters are formed on the concave portion W of cathode 120.

A gate insulating layer 132 and a gate electrode 130 are sequentiallylayered on the amorphous silicon layer 122. The gate insulating layer132 has a cavity C (or aperture) of a predetermined diameter. The gateelectrode 130 has a gate aperture 130 a corresponding to the cavity C.

The gate insulating layer 132 is a layer for maintaining electricalinsulation between the gate electrode 130 and the cathode electrode 120.The gate insulating layer 132 is made of an insulating material, such assilicon oxide (SiO₂), and generally has a thickness of at least 1 μm.

The gate electrode 130 can be made of chromium with a thickness of about0.25 μm. The gate electrode 130 extracts electron beams from the CNTemitters 150. A predetermined gate voltage, for example 80 V, can beapplied to the gate electrode 130.

In FIG. 4, reference E represents the electron beams emitted from theCNT emitters 150 when voltages are applied to the gate electrode 130 andto the cathode electrode 120. Reference F represents an equipotentialsurface in the electric field generated by the cathode electrode 120having a curved surface. The electron beams E emitted from the CNTemitters 150 proceed perpendicularly to the equipotential surface F inthe electric field, thus allowing the focusing of the emitted electrons.

Turning now to FIG. 5. FIG. 5 is a simulation of the trajectories ofelectron beams emitted from electron emitters 150 in the field emissiondevice 100 of FIG. 4. Referring to FIG. 5, the electron beams arefocused before they escape from the gate electrode 130.

Turning now to FIG. 6, FIG. 6 is a schematic cross-sectional viewillustrating a field emission device 200 according to a secondembodiment of the present invention. Referring to FIG. 6, an insulatinglayer 212 having a concave portion W and a cathode electrode 220 aresequentially formed on a glass substrate 210.

The insulating layer 212, such as a silicon oxide layer, is formed togenerate the concave portion W for the cathode electrode 220.Alternatively, the cathode electrode 220 having a concave portion can bedirectly formed on the glass substrate 210, without using the insulatinglayer 212. The insulating layer 212 can have a thickness of 2 to 10 μm.

The cathode electrode 220 can be an ITO (indium tin oxide) transparentelectrode. An amorphous silicon layer 222 is formed on portions of thecathode electrode 220 outside of the concave portion W of cathodeelectrode 220. The amorphous silicon layer 222 ensures a uniform currentflow through the cathode electrode 220. In addition, the amorphoussilicon layer 222 has the specific optical properties that allow visiblelight to pass, but blocks UV light. The amorphous silicon layer 222functions as a photolighographic mask in a back exposure to UV light, asdescribed below. CNT (carbon nano tube) emitters 250 as electronemitters are formed on the concave portion W of cathode electrode 220.

A lower gate insulating layer (or gate insulating layer) 232, a lowergate electrode (or gate electrode) 230, a focusing gate insulating layer242, and a focusing gate electrode 240 are sequentially layered on theamorphous silicon layer 222. The lower gate insulating layer 232 and thefocusing gate insulating layer 242 have a cavity C. The lower gateelectrode 230 has a lower gate aperture 230 a corresponding to thecavity C. The focusing gate electrode 240 has a focusing gate aperture240 a corresponding to the cavity C.

The lower gate insulating layer 232 is a layer for maintainingelectrical insulation between the lower gate electrode 230 and thecathode electrode 220. The lower gate insulating layer 232 is made of aninsulating material, such as silicon oxide (SiO₂), and generally has athickness of at least 1 μm.

The lower gate electrode 230 can be made of chromium with a thickness ofabout 0.25 μm. The lower gate electrode 230 extracts electron beams fromthe CNT emitters 250. A predetermined gate voltage, for example 80 V,can be applied to the lower gate electrode 230.

The focusing gate insulating layer 242 is a layer for insulating thelower gate electrode 230 from the focusing gate electrode 240. Thefocusing gate electrode 240 can be made of a silicon oxide (SiO₂) with athickness of at least 1 μm.

The focusing gate electrode 240 can be made of chromium with a thicknessof about 0.25 μm. The focusing gate electrode 240 is supplied with avoltage lower than that of the lower gate electrode 230, and serves tofocus the electron beams emitted from the CNT emitters 250.

FIG. 7 is a simulation of the trajectories of electron beams emittedfrom electron emitters of the field emission device of FIG. 6. Referringto FIG. 7, the electron beams are focused before they pass through thelower gate electrode 230 and again focused while escaping from thefocusing gate electrode 240.

FIG. 8 is a schematic cross-sectional view illustrating the structure ofa field emission display (FED) employing a novel field emission deviceaccording to the present invention. Some constituent elements that aresubstantially identical to those illustrated in FIG. 6 are referred toby the same name and will not be described again in detail.

Referring to FIG. 8, the FED includes a front substrate 370 and a rearsubstrate 310 spaced apart from each other by a predetermined distance.A spacer (not shown) is provided between the front substrate 370 and therear substrate 310 to fix the distance between the front substrate 370and the rear substrate 310. The front substrate 370 and the rearsubstrate 310 can be made of glass.

A field emitting portion is formed on the rear substrate 310, and alight emitting portion is formed on the front substrate 370. Theelectrons emitted from the field emitting portion cause light to beemitted from the light emitting portion.

Specifically, an insulating layer 312 having a concave portion W isformed on the rear substrate 310. A plurality of cathode electrodes 320are formed on the concave portions W of the insulating layer 312 and arearranged in parallel to each other and spaced apart from each other by apredetermined spacing and in a predetermined pattern, for example, inthe form of stripes. As the cathode electrodes 320 also have concaveportions W that correspond to the concave portions W in insulating layer312

An amorphous silicon layer 322 is formed on the insulating layer 312 andis perforated by a aperture exposing the concave portion W of thecathode electrode 320. A lower gate insulating layer 332, a lower gateelectrode 330, a focusing gate insulating layer 342, and a focusing gateelectrode 340 are sequentially formed on the amorphous silicon layer322, each also being perforated by a aperture and forming apredetermined cavity C above the concave portion W. Electron emitters,for example, CNT emitters 350, are formed on concave portion W ofcathode electrode 320.

An anode electrode 380 is formed on the front substrate 370, and afluorescent layer 390 is coated on the anode electrode 380. A blackmatrix 392, for increasing color purity, is located on the anodeelectrode 380 between the fluorescent layers 390.

Now, the operation of a FED having the above structure will be describedin detail with reference to the attached drawings. An anode voltage Va,of 2.5 kV pulses, is applied to the anode electrode 380, a gate voltageVg of 80 V is applied to the lower gate electrode 330, and a focusinggate voltage Vf of 30 V is applied to the focusing gate electrode 340.At this time, electrons are emitted from the CNT emitters 350 due to thegate voltage Vg. The emitted electrons are focused before escaping thelower gate electrode 330, due to the concave shape of the cathodeelectrode 320, and are again focused due to the focusing gate voltage Vfof focusing gate electrode 340. Because the electrons are properlyfocused, the focused electrons excite the fluorescent layer 390 at thedesired location. Thus, the fluorescent layer 390 emits a predeterminedvisible light 394.

Turning now to FIG. 9, FIG. 9 is a simulation of the trajectories ofelectron beams emitted from electron emitters 350 in the FED 300illustrated in FIG. 8. Referring to FIG. 9, it can be seen that theelectron beams emitted from the FED 300 are focused on the desired pixelon the anode electrode 380. Thus, the FED 300 using a field emissiondevice according to the present invention can provide improved colorpurity.

Next, the process of producing the novel field emission device 200 ofFIG. 6 according to an embodiment of the present invention will bedescribed in detail with reference to FIGS. 10 through 22. Turning nowto FIG. 10, a silicon oxide layer is formed to a thickness of at least 1μm to become insulating layer 412 on a glass substrate 410 using PECVD(plasma enhanced chemical vapor deposition). Then, a first photoresistfilm P1 is coated on the insulating layer 412, and the first photoresistfilm P1 is exposed to UV light. Front exposure or back exposure can beperformed by using a separate mask (not shown). UV light enters aportion corresponding to the concave portion W as illustrated in FIG. 6of the first photoresist film P1. That is, only a region P1 a located onthe top of the concave portion W of the first photoresist film P1 isexposed to UV light. The exposed region P1 a is removed via a developingoperation. Then, baking is performed to harden the patterned photoresistlayer P1.

Turning now to FIG. 11, FIG. 11 illustrates the product of the abovedeveloping and baking operations. The insulating layer 412 is exposed atthe removed region P1 a. Turning now to FIG. 12, a wet etching of theinsulating layer 412 is performed using the patterned first photoresistfilm P1 as an etch mask. This wet etch forms hemispherical concaveportion W or well. Then, the first patterned photoresist film P1 isremoved. The location of the concave portion W corresponds to that ofthe CNT emitters (150 as illustrated in FIG. 6). The concave portion Whas a diameter of at least 3 μm.

Turning now to FIG. 13, a cathode electrode 420 of preferablytransparent ITO is formed on the insulating layer 412 by sputtering.Then, an amorphous silicon layer 422 is formed on the cathode electrode420 using PECVD. Then, a second photoresist film P2 is coated on theamorphous silicon layer 422, and region P2 a corresponding to theconcave portion W is exposed to light and developed. A portion of theamorphous silicon layer 422 is exposed through removed region P2 a. Wetetching is performed on the open portion of the amorphous silicon layer422 using the second photoresist film P2 as an etch mask. FIG. 14illustrates the result of the wet etching and after the secondphotoresist film P2 is removed.

Referring now to FIG. 15, after removal of the second photoresist filmP2, a lower gate insulating layer 432 is formed on the amorphous siliconlayer 422 filling the concave portion W. The lower gate insulating layer432 is made of a silicon oxide having a thickness of at least 1 μm.Then, a lower gate electrode 430 is formed on the lower gate insulatinglayer 432. The lower gate electrode 430 is made of chromium and isapplied by sputtering, to a thickness of about 0.25 μm. Next, a thirdphotoresist film P3 is formed over the lower gate electrode 430, andregion P3 a corresponding to the concave portion W is exposed to light.

Subsequently, the exposed region P3 a is removed by developing. Aportion of the lower gate electrode 430 is exposed via the removedregion P3 a. Wet etching is performed on the exposed portion of thelower gate electrode 430 using the patterned third photoresist film P3as an etch mask.

Turning now to FIG. 16, FIG. 16 illustrates the resultant product afterthe wet etching of the exposed portion the lower gate electrode 430 andafter the removal of third photoresist film P3. FIG. 16 illustrates alower gate aperture 430 a formed in lower gate electrode 430.

Referring now to FIG. 17, after removal of the third photoresist filmP3, a focusing gate insulating layer 442 is formed on the lower gateinsulating layer 432 filling the lower gate aperture 430 a and over thelower gate electrode 430. The focusing gate insulating layer 442 iscomposed of a silicon oxide having a thickness of at least 1 μm. Then, afocusing gate electrode 440 is formed on top of the focusing gateinsulating layer 442. The focusing gate electrode 440 is made ofchromium and is applied by sputtering and has a thickness of about 0.25μm. Next, a fourth photoresist film P4 is formed on the focusing gateelectrode 440 and region P4 a corresponding to the concave portion W isexposed to light.

Subsequently, the exposed region P4 a is removed by developing. Aportion of the focusing gate electrode 440 is exposed via the removedregion P4 a. Wet etching is performed on the open portion of thefocusing gate electrode 440 using the fourth photoresist film P4 as anetch mask.

Turning now to FIG. 18, FIG. 18 illustrates the result, with the fourthphotoresist film P4 removed after wet etching the exposed portion of thefocusing gate electrode 440. A focusing gate aperture 440 a is formed.Referring to FIG. 19, after removal of the fourth photoresist film P4, afifth photoresist film P5 is coated on the patterned focusing gateelectrode 440. Then, region P5 a corresponding to the concave portion Wand focusing gate aperture 440 a is exposed to light. At this time, backexposure can be performed by irradiating UV light toward the substrate410 from below. Since the amorphous silicon layer 422 blocks UV light,only region P5 a corresponding to the concave portion W of the fifthphotoresist film P5 is exposed to the UV light. Thus, amorphous siliconlayer 422 serves as a photolithography mask.

After exposure, the exposed region P5 a is removed by developing. Wetetching is performed on the focusing gate insulating layer 442 and thelower gate insulating layer 432 using the fifth photoresist film P5 asan etching mask, to open the concave portion W to expose the cathodeelectrode 420. FIG. 20 illustrates the result after the wet etching andafter the removal of the fifth photoresist film P5.

Referring now to FIG. 21, a CNT paste 452 containing a negativephotosensitive substance is coated on the exposed concave portion W ofcathode electrode 420. Then a back exposure is performed on thephotosensitive CNT paste 452 using the amorphous silicon layer 422 as aphotolithography mask. Then, CNT emitters 450 are formed on the concavecathode electrode 420 by developing and baking operations, to result inthe structure illustrated in FIG. 22.

The above process of producing the field emission device produces thefield emission device 200 illustrated in FIG. 6. The field emissiondevice 100 illustrated in FIG. 4 can be produced by an equivalentprocess, but by omitting the forming the focusing gate insulating layerand the focusing gate electrode.

In the embodiments of the present invention, the CNT emitters are formedusing a printing method, but the present invention is in no way solimited. For example, the CNT can be grown by forming a catalytic metallayer on the concave portion W of the cathode electrode 420 and thendepositing a carbon containing gas, such as methane gas on to thecatalytic metal layer. The forming the insulating layer 412 and theforming the cathode electrode 420 can instead be performed by formingthe concave portion W directly on the cathode electrode 420, instead ofon the insulating layer 412.

As described above, in the field emission devices according to thepresent invention, the cathode electrode has a concave portion and CNTemitters are formed on the concave portion, thus increasing theefficiency of focusing electrons emitted from the CNT emitters. Thus,the resulting FED employing the novel field emission device can provideimproved color purity.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A field emission device, comprising: a glass substrate; a materiallayer arranged on the glass substrate and having a concave portion; acathode electrode arranged on the material layer, the cathode electrodehaving a concave portion; a plurality of electron emitters arranged onthe concave portion of the cathode electrode; a gate insulating layerarranged on the cathode-electrode and having a cavity communicating withthe concave portion of the cathode electrode; and a gate electrodearranged on the gate insulating layer and having a gate aperture alignedwith the cavity.
 2. The field emission device of claim 1, the cavitybeing of a hemispherical shape.
 3. The field emission device of claim 1,the material layer comprises an insulating layer.
 4. The field emissiondevice of claim 1, the material layer comprises a metal layer.
 5. Thefield emission device of claim 4, the metal layer comprises a samematerial as the cathode electrode.
 6. The field emission device of claim1, further comprising an amorphous silicon layer arranged between thecathode electrode and the gate insulating layer, the amorphous siliconlayer being perforated by a aperture that is aligned with the concaveportion of the cathode electrode.
 7. The field emission device of claim1, the plurality of electron emitters comprises carbon nanotube (CNT)emitters.
 8. A field emission device, comprising: a glass substrate; amaterial layer arranged on the glass substrate and having a concaveportion; a cathode electrode arranged on the material layer, the cathodeelectrode having a concave portion; a plurality of electron emittersarranged on the concave portion of the cathode electrode; a lower gateinsulating layer arranged on the cathode electrode and having a cavitycommunicating with the concave portion of the cathode electrode; a lowergate electrode arranged on the lower gate insulating layer and having alower gate aperture aligned with the cavity; a focusing gate insulatinglayer arranged on the lower gate electrode and having an aperturecommunicating with the cavity; and a focusing gate electrode arranged onthe focusing gate insulating layer and having a focusing gate aperturealigned with the cavity.
 9. The field emission device of claim 8, thecavity having a shape of a hemisphere.
 10. The field emission device ofclaim 8, the material layer comprises an insulating layer.
 11. The fieldemission device of claim 8, the material layer comprises a metal layer.12. The field emission device of claim 11, the metal layer comprises asame material as the cathode electrode.
 13. The field emission device ofclaim 8, further comprising an amorphous silicon layer arranged betweenthe cathode electrode and the lower gate insulating layer and having anaperture aligned with the concave portion of the cathode electrode. 14.The field emission device of claim 8, the plurality of electron emitterscomprises carbon nanotube (CNT) emitters.
 15. A field emission display(FED), comprising: a rear substrate; a material layer arranged on therear substrate and having a concave portion; a cathode electrodearranged on the material layer, the cathode electrode having a concaveportion; a plurality of electron emitters arranged on the concaveportion of the cathode electrode; a gate insulating layer arranged onthe cathode electrode and having a cavity communicating with the concaveportion of the cathode electrode; a gate electrode arranged on the gateinsulating layer and having a gate aperture aligned with the cavity; afront substrate spaced apart from the rear substrate by a predetermineddistance; an anode electrode arranged on a side of the front substratefacing a plurality of electron emitters; and a fluorescent layerarranged on the anode electrode.
 16. The FED of claim 15, the cavityhaving a shape of a hemisphere.
 17. The FED of claim 15, the materiallayer comprises an insulating layer.
 18. The FED of claim 15, thematerial layer comprises a metal layer.
 19. The FED of claim 18, themetal layer comprises a same material as the cathode electrode.
 20. TheFED of claim 15, further comprising an amorphous silicon layer arrangedbetween the cathode electrode and the gate insulating layer, theamorphous silicon layer having an aperture corresponding to the concaveportion of the cathode electrode.
 21. The FED of claim 15, the pluralityof electron emitters comprises carbon nanotube (CNT) emitters.
 22. Afield emission display (FED), comprising: a rear substrate; a materiallayer arranged on the rear substrate and having a concave portion; acathode electrode arranged on the material layer, the cathode electrodehaving a concave portion; a plurality of electron emitters arranged onthe concave portion of the cathode electrode; a lower gate insulatinglayer arranged on the cathode electrode and having a cavitycommunicating with the concave portion of the cathode electrode; a lowergate electrode arranged on the lower gate insulating layer and having alower gate aperture aligned with the cavity; a focusing gate insulatinglayer arranged on the lower gate electrode and having an aperturecommunicating with the cavity; a focusing gate electrode arranged on thefocusing gate insulating layer and having a focusing gate aperturealigned with the cavity; a front substrate spaced apart from the rearsubstrate by a predetermined distance; an anode electrode arranged on aside of the front substrate facing the plurality of electron emitters;and a fluorescent layer arranged on the anode electrode and facing theplurality of electron emitters.
 23. The FED of claim 22, the cavityhaving a shape of a hemisphere.
 24. The FED of claim 22, the materiallayer comprises an insulating layer.
 25. The FED of claim 22, thematerial layer comprises a metal layer.
 26. The FED of claim 25, themetal layer comprises a same material as the cathode electrode.
 27. TheFED of claim 22, further comprising an amorphous silicon layer arrangedbetween the cathode electrode and the lower gate insulating layer, theamorphous silicon layer having an aperture corresponding to the concaveportion of the cathode electrode.
 28. The FED of claim 22, the pluralityof electron emitters comprises carbon nanotube (CNT) emitters.